Plasma processing systems are widely used in a variety of industries for modifying the surface properties of materials. For example, the manufacture of modern integrated circuits generally involves many processing steps that use plasmas for etching of submicrometer features, and/or for depositing atomically thin layers of materials.
A typical plasma processing system comprises a processing chamber and a power delivery system that creates and maintains the plasma inside the chamber. Electrically, the plasma is a load with a characteristic impedance that is affected by the power generator. And in addition, the impedance of a processing plasma may vary depending upon process conditions or other variables. Variations in plasma impedance may adversely affect the power delivery from the generator, which typically provides optimal power delivery only for a particular load impedance. These variations may also result in undesired drifts or perturbations in process variables, such as etch or deposition rates, due to changes in the physical properties of the plasma at different power levels. As a result, plasma processing systems are often equipped with impedance matching and control mechanisms or circuitry that respond to changes in plasma impedance and maintain desired levels of power delivery to the plasma.
As film thicknesses and feature sizes continually shrink, plasma sources and processes also must evolve in order to deliver the control and precision needed for new and next generation devices and coatings. Power delivery is becoming increasingly critical in RF driven systems as trends continue toward lower pressures, lower powers and larger electrode areas. Especially in etching and deposition processes, commonly using electronegative species, the combined effects of low pressure, low power density and electro-negativity often lead to increased risk of plasma instabilities.